Welded piston assembly

ABSTRACT

A pre-finished piston part is disclosed that may be used to form a piston assembly. A pre-finished piston may include a lower part defining a piston axis, the lower part having a skirt and forming a lower surface of a cooling gallery. The lower part may include a radially inner bowl surface defining a lower part radially inner mating surface. The pre-finished piston assembly may further include an upper part having a radially outer bowl surface meeting the radially inner bowl surface at a radially inner joint. The upper part may include a radially inner wall defining a radially inner upper part mating surface. The radially inner wall may define a radially inwardly facing surface that defines a non-parallel angle with the radially inner bowl surface where the radially inner bowl surface meets the radially innermost edge of the radially inner mating surface.

BACKGROUND

Internal combustion engine manufacturers are constantly seeking toincrease power output and fuel efficiency of their products. Oneapproach to generally increasing efficiency and power is to reduce theoscillating mass of an internal combustion engine, e.g., of the pistons,connecting rods, and other moving parts of the engine. Engine power mayalso be increased by raising the compression ratio of the engine.Raising the compression ratio of an engine also generally raises thepressure and temperature within the combustion chamber during operation.

As a result of the weight reductions in combination with increasedpressures and temperatures associated with operation, engines, and inparticular the pistons of the engine, are under increased stress. Pistoncooling is therefore increasingly important for withstanding theincreased stress of such operational conditions over the life of theengine.

To reduce the operating temperatures of piston components, a coolinggallery may be provided about a perimeter of the piston. A coolant suchas crankcase oil may be introduced to the cooling gallery, and may bedistributed about the cooling gallery by the reciprocating motion of thepiston, thereby reducing the operating temperature of the piston.

At the same time, the cooling galleries may increase overall complexityof the piston assembly and manufacturing of the same. For example,cooling galleries may require additional component, such as a coolinggallery cover, to encourage proper circulation of a coolant throughoutthe cooling gallery by temporarily retaining coolant (e.g., oil) that iscirculated through the cooling gallery. The additional components suchas cover plates also add complexity, however. Additionally, coolinggalleries may be expensive and/or difficult to form in smaller pistonapplications such as in the case of lightweight or light duty pistons.

Accordingly, there is a need for a piston that is practical forproduction in a mass manufacturing environment, while also allowingadequate cooling, such as by providing a cooling gallery.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, illustrative examples are shown indetail. Although the drawings represent the exemplary illustrationsdescribed herein, the drawings are not necessarily to scale and certainfeatures may be exaggerated to better illustrate and explain aninnovative aspect of an exemplary illustration. Further, the exemplaryillustrations described herein are not intended to be exhaustive orotherwise limiting or restricting to the precise form and configurationshown in the drawings and disclosed in the following detaileddescription. Exemplary illustrations of the present invention aredescribed in detail by referring to the drawings as follows:

FIG. 1A is a perspective view of an exemplary piston assembly;

FIG. 1B is a partial section view of the exemplary piston assembly ofFIG. 1A;

FIG. 1C is a section view of the exemplary piston assembly of FIG. 1A,taken at ninety degrees with respect to the section of FIG. 1B;

FIG. 2A is a partial section view of an exemplary piston upper part andpiston lower part;

FIG. 2B is a partial section view of an exemplary piston upper part andpiston lower part, taken at ninety degrees with respect to the sectionof FIG. 1B;

FIG. 3A is an enlarged section view of a cooling gallery area of apiston upper part and lower part;

FIG. 3B is an enlarged section view of a cooling gallery area of thepiston upper part and lower part of FIG. 3A, after an exemplary weldingprocess;

FIG. 4A is a section view of an exemplary piston upper part and lowerpart after an exemplary welding process;

FIG. 4B is a section view of an exemplary piston upper part and lowerpart after an exemplary welding process, taken at ninety degrees withrespect to the section of FIG. 4A;

FIG. 5 is a section view of an exemplary piston upper part and lowerpart after an exemplary welding process; and

FIG. 6 is a process flow diagram for a method of making a pre-finishedpiston, according to an exemplary illustration.

DETAILED DESCRIPTION

Reference in the specification to “an exemplary illustration”, an“example” or similar language means that a particular feature,structure, or characteristic described in connection with the exemplaryapproach is included in at least one illustration. The appearances ofthe phrase “in an illustration” or similar type language in variousplaces in the specification are not necessarily all referring to thesame illustration or example.

Various exemplary illustrations are provided herein of a pre-finishedpiston part that may be used to form a piston assembly. A pre-finishedpiston may include a lower part defining a piston axis, the lower parthaving a skirt and forming a lower surface of a cooling gallery. Thelower part may include a radially inner bowl surface defining a lowerpart radially inner mating surface, and a radially outer wall defining aradially outer mating surface. The pre-finished piston assembly mayfurther include an upper part having a radially outer bowl surfacemeeting the radially inner bowl surface at a radially inner joint. Theupper part may include a radially inner wall defining a radially innerupper part mating surface, and a radially outer wall defining an upperpart radially outer mating surface. The radially inner wall may define aradially inwardly facing surface that defines a non-parallel angle withthe radially inner bowl surface where the radially inner bowl surfacemeets the radially innermost edge of the radially inner mating surface.

Exemplary methods may include a method of forming a pre-finished pistonassembly. An exemplary method may include providing a lower partdefining a piston axis, the lower part having a skirt and forming alower surface of a cooling gallery, the lower part having a radiallyinner bowl surface defining a lower part radially inner mating surface,the lower part including a radially outer wall defining a radially outermating surface. The method may further include abutting the lower partagainst an upper part, the upper part having a radially outer bowlsurface meeting the radially inner bowl surface at a radially innerjoint, the upper part including a radially inner wall defining a lowersurface extending radially to define an upper part radially inner matingsurface, the upper part including a radially outer wall defining anupper part radially outer mating surface. The method may further includewelding the radially inner mating surfaces together, wherein a radiallyinwardly facing surface of the upper part defines a non-parallel anglewith the radially inner bowl surface where the radially inner bowlsurface meets the radially innermost edge of the radially inner matingsurface.

Turning now to FIGS. 1A, 1B, and 1C, an exemplary piston assembly 100 isillustrated. Piston assembly 100 may include a piston body 102 and acooling gallery ring 104 that is joined with the body 102. The pistonbody 102 and cooling gallery ring 104 may cooperate to define acombustion bowl 122. The body 102 may include a ring belt portion 106that is configured to seal against an engine bore (not shown) receivingthe piston assembly 100. For example, the ring belt portion 106 maydefine one or more circumferential grooves that receive piston rings(not shown), which in turn seal against engine bore surfaces duringreciprocal motion of the piston assembly 100 within the engine bore. Thecooperation of the cooling gallery ring 104 and body 102 in defining thecombustion bowl 122, as well as other features of the piston 100described below, may generally allow flexibility in regard to the sizeand shape of the piston 100 and components thereof, e.g., coolinggallery ring 104 and/or the piston body 102. Merely as one example, alower overall compression height and/or center of gravity of the pistonassembly 100 may be achieved as a result of the configuration of aradially inner joint between the cooling gallery ring 104 and body 102during an associated forming process, as will be described furtherbelow.

The piston body 102 may include a skirt surface 103 that generallysupports the piston assembly 100 during engine operation, e.g., byinterfacing with surfaces of an engine bore (not shown) to stabilize thepiston assembly 100 during reciprocal motion within the bore. Forexample, the skirt surface 103 may generally define a circular outershape about at least a portion of a perimeter of the piston assembly100. The outer shape may correspond to the engine bore surfaces, whichmay be generally cylindrical.

The body 102 may also define piston pin bosses 105. The piston pinbosses 105 may generally be formed with apertures 107 configured toreceive a piston pin (not shown). For example, a piston pin may beinserted through the apertures in the piston pin bosses 105, therebygenerally securing the piston 100 to a connecting rod (not shown).

Turning now to FIGS. 1B and 1C, the body 102 and cooling gallery ring104 may cooperate to define a cooling gallery 108. The cooling gallery108 generally extends about a perimeter of the piston crown, and maycirculate a coolant during operation, e.g., engine oil, thereby reducingan operating temperature of the piston. Additionally, the circulation ofthe coolant may facilitate the maintaining of a more stable or uniformtemperature about the piston 100, and especially in the upper portion ofthe piston assembly 100, e.g., adjacent the combustion bowl 122.

The piston body 102 and ring 104 may be fixedly joined, e.g., in awelding process. By fixedly joining the piston body 102 and ring 104,the piston assembly 100 is generally formed as a one-piece or “monobloc”assembly. As will be described further below, the body 102 and ring 104components may be joined along both radially inner and outer interfaceregions I, O in a welding process. Accordingly, the piston body 102 maybe generally unitized with the cooling gallery ring 104, such that eachis immovable relative to the other after securement to the crown,although the body 102 and ring 104 are separate components.

The cooling gallery ring 104 may be secured to the body 102 such thatthe crown 102 and the skirt 104 cooperate to form a generally continuousupper combustion bowl surface 122 of the piston assembly 100. Forexample, as will be described further below, corresponding matingsurfaces of the body 102 and cooling gallery ring 104 may meet withinthe combustion bowl 122 along a radially inner interface region I suchthat the piston body 102 defines a radially inner portion 122 a of thecombustion bowl 122, while the cooling gallery ring 104 defines aradially outer portion 122 b of the combustion bowl 122. The radiallyouter interface region O may be positioned along the ring belt portion106.

The piston body 102 and the cooling gallery ring 104 may be secured orfixedly joined to one another in any manner that is convenientincluding, but not limited to, welding methodologies such as frictionwelding, beam welding, laser welding, soldering, or non-weldingmethodologies such as adhesive bonding, merely as examples. In oneexample, the piston crown and skirt are joined in a welding process,e.g., friction welding. In another exemplary illustration, respectivemating surfaces of a lower piston part corresponding to piston body 102,and of an upper piston part corresponding to cooling gallery ring 104,may be joined in a friction welding process or adhesive bonding process,merely as examples, thereby securing the piston body 102 and coolinggallery ring 104 together.

Turning now to FIGS. 2A, and 2B, an exemplary friction welding processassociated with piston 100 is explained in further detail. Piston 100may generally be formed from an upper piston part 104′ corresponding tocooling gallery ring 104, and a lower piston part 102′ corresponding topiston body 102. For example, the upper and lower piston parts 104′,102′ may generally have the features shown corresponding to the piston100, e.g., upper and lower interior surfaces 111, 113 corresponding tothe cooling gallery 108. Moreover, the upper and lower piston parts104′, 102′ may generally be suitable for joining to each other, e.g.,via a friction welding process, while they may not have finishedexternal surfaces or features of the piston 100 such as the ringgrooves, combustion bowl 122, etc. seen above in piston assembly 100.

Accordingly, the upper and lower piston parts 104′, 102′ may generallybe joined together, e.g., in a friction welding operation, to form apre-finished piston component 100′ as will be described further below,and as best seen in FIGS. 3A, 3B, 4A, 4B, and 5. The pre-finished pistoncomponent may subsequently be finished, e.g., in a machining operation,to provide finished surface details required for the piston 100, e.g.,ring grooves and the final shape or contour of the combustion bowl 122.Accordingly, the general shape of the final piston assembly 100 isillustrated in phantom in FIGS. 4A, 4B, and 5, in contrast to theinitial shape defined by the pre-finished piston part 100′.

As best seen in FIGS. 2A and 2B, mating surfaces 114, 116 of the upperpiston part 104′ may be secured to respective mating surfaces 118, 120of the lower piston part 102′ in any manner that is convenient, e.g., byway of a welding operation such as friction welding or adhesive bonding,merely as examples, thereby securing the upper piston part 104′ and thelower piston part 102′ together. Piston parts 102′, 104′ are illustratedin further detail in FIGS. 3A, 3B, 4A, 4B, and 5 after an exemplaryfriction welding process.

The upper part 104′ and lower part 102′ may initially be rotated at highspeed relative to one another, and then placed together under highpressure as illustrated in FIG. 3A. Such a friction welding process mayform weld curls 124, 126, 128, and 130 between the upper piston part104′ and lower piston part 102′, as best seen in FIGS. 3B, 4A, and 4B.More specifically, weld curls 124, 126 may be formed that extendradially inwardly and outwardly, respectively, from the radially innerinterface region I. Additionally, weld curls 128, 130 may be formed thatextend radially inwardly and outwardly, respectively, from the radiallyouter interface region O.

As best seen in FIGS. 3B, 4A, 4B, 5A, and 5B, the weld curl 124extending radially inwardly from the radially inner interface region Imay generally form a single curl 124 extending radially inwardly andupwardly from the mating surfaces 118, 120 of the piston upper and lowerparts 104′, 102′. By contrast, the weld curls 126, 128, and 130 eachinclude respective upper and lower curl portions. More specifically, asbest seen in FIG. 3B, weld curl 128 includes an upper curl 128 a and alower curl 128 b, and weld curl 130 includes an upper curl 130 a andlower curl 130 b. Typically, during a friction welding process, an upperand lower curl, e.g., upper curl 128 a and lower curl 128 b, maygenerally form in equal measure and shape from material of theassociated mating surfaces, e.g., mating surfaces 114, 116. Thegenerally equal weld curl portions 128 a, 128 b, 130 a, 130 b may resultin part from the generally equal radial widths of the associated matingsurfaces 114, 116, and the alignment of the mating surfaces 114, 116substantially perpendicular to the piston axis (not shown in FIG. 3B).

By contrast, the generally single, upwardly extending weld curl 124 mayresult in part from a difference in widths W₁, W₂ between the associatedmating surfaces 116, 120, respectively, along the radially innerinterface region I. The mating surfaces 116, 120 may be defined bycorresponding wall members 170, 172 of the piston upper part 104′ andpiston lower part 102′, respectively. Additionally, the mating surfaces114, 118 may be defined by corresponding wall members 174, 176 of thepiston upper part 104′ and piston lower part 102′, respectively. Morespecifically, while the weld curl 126 extending radially outwardly fromthe mating surfaces 118, 120 may form into two distinct upper and lowercurl portions 126 a, 126 b in a similar fashion as the weld curls 128,130, the weld curl 124 generally includes a single curl which extendsupwardly and radially inwardly from the associated mating surfaces 118,120. The weld curl 124 may form into a single curl portion 124 a as aresult of welded material from the mating surfaces 118, 120 being forcedto flow upwards by the radially inwardly extending mating surface 120.More specifically, as material from the mating surfaces 118, 120 meltsduring the friction welding process, material forming the weld curl 124is forced to flow upwardly and cannot curl downward due to the radiallyinwardly extending mating surface 120. Thus, material forming the weldcurl 124 is forced to flow upwards and radially inwardly from the matingsurface 118 forming the single weld curl 124.

In another exemplary illustration, as best seen in FIG. 3A the matingsurface 120 extends radially inwardly from the radially inner interfaceregion I. More specifically, the mating surface 120 may extend radiallyinwardly from a radially innermost edge of the mating surface 118 of theupper part 104. The radially inwardly extending mating surface 120 maygenerally force material flow from the welded joint to flow upwards,resulting in a single weld curl 124 extending radially inwardly from theradially inner interface region I. Moreover, the mating surface 120 mayextend generally perpendicular to a radially inner surface 132 definedby the radially inner wall portion 140 of the piston upper part 104′, asbest seen in FIGS. 3A and 3B.

Turning now to FIGS. 5A and 5B, which is an enlarged view of the upperportion of the exemplary piston 100 and pre-finished piston assembly100′, the shallow bowl construction is illustrated in further detail. Asnoted above, the outer contour shown in the FIG. 5 indicates the contourof the pre-finished piston assembly 100′, prior to any finishingoperations, e.g., machining, used to form the final configuration of thepiston assembly 100, which is illustrated in phantom lines. Due to themismatched widths of the radially inner mating surfaces 118, 120, i.e.,as a result of the radially inward mating surface 120 extending awayfrom the interface region I, a single weld curl 124 is formed thatgenerally curls upwardly and radially inwardly from the radially innerinterface region I, as briefly described above.

Moreover, as seen in FIG. 5, the cooling gallery 108 generally extendsradially inwardly with respect to a radially outermost point 152 alongthe combustion bowl 122 of the final configuration of the pistonassembly 100. In other words, a radially innermost point 150 of thecooling gallery 108 is spaced radially inwardly from a radiallyoutermost point 152 of the combustion bowl 122 of the piston assembly100 by a radial distance D. The enlarged cooling gallery 108 therebyprovides enhanced cooling to the piston 100.

The radially inward spacing D between the points 150, 152 may befacilitated at least in part by the illustrated geometry of the lowercooling gallery surface 113 and orientation of the radially innerinterface region I. More specifically, as seen in FIG. 5 an uppermostregion 154 of the cooling gallery surface 113 of the lower part 102′extends axially downward at an initial angle α with respect to an axisA-A of the piston 100. As illustrated in FIG. 5, the uppermost region154 may define a linear or substantially linear path leading directlyfrom the mating surface 120 downward with respect to the pre-finishedpiston 100′ at the angle α. The cooling gallery surface 113 maytransition to a second angle β with respect to the piston axis A-A,transitioning to the second angle β at an apex 180. More specifically, asecond region 156 of the cooling gallery surface 113 may define a linearor substantially linear path from the apex 180 downward with respect tothe pre-finished piston 100′ at the angle β. The apex 180 may have anaxial height with respect to the pre-finished piston 100′ correspondingapproximately to the axial position of the outer mating surfaces 114,118, e.g., as seen in FIG. 5. The angle β may be greater with respect tothe piston axis A-A than the initial angle α. In one exemplaryillustration, the angle α is no greater than twenty (20) degrees, whilethe angle β is larger than angle β but is no larger than approximatelyforty-five (45) degrees.

By contrast, in previous friction welding approaches for pistons,surfaces of wall members adjacent mating surfaces of the upper and lowerparts used to form the piston typically extend in a substantiallyparallel fashion above and below mating surfaces, due to the generallylarge magnitude forces that act upon the mating surfaces and the need tosupport the mating surfaces to a maximum extent possible. However, thewalls extending parallel above and below the joint generally alsoincreases an overall height of the upper piston part, resulting in agreater compression height of the piston overall. Additionally, previousfriction welding approaches in pistons have generally required thatcomponents be rotationally symmetrical in order to allow joining thecylindrical parts by rotation at high speeds. By comparison, the variedwidths W₁, W₂ of the mating surfaces 116, 120, respectively may beemployed herein, resulting in the formation of a single weld curl 124that may be subsequently removed, as further described below.

Referring again to the exemplary pre-finished piston part 100′ andassociated piston 100, the exemplary angles α and β have been found togenerally provide sufficient support to the mating surfaces 116, 120 ofthe radially inner interface region I while allowing increased overallvolume of the cooling gallery 108 and also a shorter overall height ofthe upper piston part 104′. The shorter overall height may generallyresult from the ability to position the radially inner mating surfaces116, 120 axially higher with respect to a top surface 160 of the piston100, since the mating surface 120 extends radially inward from theinterface region I between the mating surfaces 116, 120, and notparallel to the piston axis as in previous piston welding approaches.Moreover, the radially inwardly extending mating surface 120 increasessupport to the radially inner interface region I, thereby inhibiting anydeformation of the piston upper part 104′ or piston lower part 102′ thatmight otherwise result from an imbalance in force application betweenthe mating surfaces 116, 120 resulting from the angled surfaces 154,156. Accordingly, the wall member 172 of the lower piston part 102′ maygenerally define non-parallel surfaces extending away from the jointbetween the radially inner mating surfaces 116, 120. By contrast, thewall members 174, 176 meeting in the radially outer interface region Omay each generally extend in similar parallel fashion with respect tothe piston axis adjacent the joint between the mating surfaces 114, 118,resulting in weld curls 128 a, 128 b, 130 a, and 130 b that aresubstantially equal in magnitude and are generally mirror images of theweld curls of the corresponding piston part.

In another exemplary illustration, the radially inwardly facing surface132 of the upper part 104′ may define a non-parallel angle with aradially inner bowl surface 122 b′ defined by the lower part 102′, whichcorresponds to the combustion bowl surface contour 122 apart from thelack of finishing the combustion bowl surface 122, e.g., in a machiningoperation. More specifically, the radially inner bowl surface 122 b′ mayextend to meet a radially innermost edge 185 of the radially innermating surface 116, at which point the radially inner bowl surface 122b′ defines a non-parallel angle with the radially inwardly facingsurface 132 of the upper part 104′. Moreover, in some exemplaryapproaches the radially inner bowl surface 122 b′ defines a right anglewith the radially inwardly facing surface 132 of the upper part 104′, orsubstantially a right angle with the radially inwardly facing surface132 of the upper part 104′.

The shorter overall height of the piston upper part 104′ reduces acompression height of the piston, which is defined here as a ratiobetween (a) the distance from a top surface of the piston and a pin boreaxis (not shown in FIG. 5) and (b) the piston diameter D. Moreover, thereduced overall height of the piston upper part 104′ results in asmaller height H of the combustion bowl 122 of the finished piston 100.In one exemplary illustration, the height H of the combustion bowl 122,as measured from upper surface 160 of the piston to a lowermost positionof the combustion bowl 122, is no greater than 15% of the pistondiameter D. Accordingly, the angled construction of the lower coolinggallery surface 113 adjacent the mating surfaces 116, 120, as well asthe radially inwardly extending mating surface 120 facilitate acombustion bowl 122 that is relatively shallow in comparison to previousapproaches, while also facilitating a reduced overall compression heightof the piston 100.

Upon completion of a friction welding process, weld flashing, e.g., weldcurls 124 and 130, may subsequently be removed from outer surfaces ofthe piston upper part 104′ and piston lower part 102′ to form therelatively smooth outer surface of the piston assembly 100. For example,weld flashing may be removed via a machining operation. Accordingly, thecombustion bowl surface 122 may be substantially smooth across aninterface between the cooling gallery ring 104 and the piston body 102,e.g., so that disruptions and/or discontinuities in the surface 122 areminimized. Moreover, the ring belt portion 106 may also be machined orotherwise worked to remove the weld curl 130 and form the ring grooves.Minimizing such disruptions or discontinuities may generally reducecracks or other loosening of an interface between the body 102 and thering 104 along the interface regions I, O during normal long-termoperation. Accordingly, any defects or failure in the combustion bowlsurface 122 and/or ring belt portion 106, e.g., due to wear occurringduring operation of an engine using piston assembly 100, may beminimized.

Cooling gallery 108 may advantageously define at least one opening (notshown) that allows for gases to escape during a friction weldingprocess. Additionally, the opening(s) may allow coolant, e.g., oil, tobe circulated through the cooling gallery during operation.

The piston body 102 and cooling gallery ring 104 may be constructed fromany materials that are convenient. In one exemplary illustration, thebody 102 and cooling gallery ring 104 are formed of different materials.In another example, the body 102 and cooling gallery ring 104 are formedof the same material, e.g., steel. Accordingly, a material used for thecomponents may be more closely matched with the general requirements andoperating conditions relevant to each. Piston body 102 may, merely asexamples, include different mechanical properties, e.g., yield point,tensile strength or notch toughness, than the cooling gallery ring 104.Any material or combination may be employed for the body 102 and coolinggallery ring 104 that is convenient. Merely as examples, the body 102and/or cooling gallery ring 104 may be formed of a steel material, castiron, aluminum material, composite, or powdered metal material. The body102 and/or cooling gallery ring 104 may also be formed in a same formingprocess type, e.g., each may be formed in a high-speed forging or coldforming process. Alternatively, the cooling gallery ring 104 and body102 may be formed in different processes, e.g., the body 102 may be agenerally single cast piece, while the cooling gallery ring 104 may beforged. Any material and/or forming combination may be employed that isconvenient.

Turning now to FIG. 6, an exemplary process 600 for making apre-finished piston assembly 100′ and/or piston assembly 100 isillustrated. Process 600 may generally begin at block 602, where apiston upper part is provided. For example, as described above a pistonupper part 104′ may include radially inner and outer mating surfaces116, 114. Additionally, the piston upper part 104′ may define at leastin part a cooling gallery 108 extending about a periphery of the pistonupper part 102′, e.g., with upper cooling gallery surface 111. Process600 may then proceed to block 604.

At block 604, inner and outer mating surfaces of the piston upper partmay be abutted with corresponding inner and outer mating surfaces of apiston lower part. For example, as described above a radially innerinterface region I may be formed between the inner mating surfaces 116,120, and a radially outer interface region O may be formed between outermating surfaces 114, 118 of the upper part 104′ and lower part 102′.Moreover, a cooling gallery 108 may be disposed between the radiallyinner and outer interface regions I, O, and may be defined in part by acooling gallery lower surface 113 defined by the piston lower part 102′.Additionally, the lower part 102′ may include a pair of oppositelydisposed pin bosses 105 defining respective piston pin bores 107.Process 600 may then proceed to block 606.

At block 606, a radially inner interface region geometry may beestablished. For example, as described above a radially inner matingsurface 120 of the lower piston part 102′ may extend radially inwardlyfrom the radially inner interface region I and/or the joint between theradially inner mating surfaces 116, 120. In one exemplary illustrationnoted above, the radially inner mating surface 120 defines substantiallya right angle with respect to radially inwardly facing surface 132 ofthe piston upper part 104′ extending away from the radially innerinterface region I and/or the joint between the mating surfaces 116,120. Alternatively or in addition, surfaces of the cooling gallerydefined by the lower part 102′ may extend away from the joint, i.e.,from the mating surface 120, in an angled fashion, thereby facilitatingan increased volume of the cooling gallery 108, with at least a portionof the cooling gallery 108 extending radially inward of at least aportion of the combustion bowl 122 of the resulting piston 100.Moreover, a reduced overall height of the piston 100 and componentsthereof may also be achieved.

Proceeding to block 608, the upper and lower piston parts 104′, 102′ maybe fixedly secured together along one or more of the radially inner andouter interface regions. For example, as described above the upper andlower piston parts 104′, 102′ may be fixedly secured together along theradially inner and/or outer mating surfaces of the crown and skirt byfriction welding, adhesive bonding, or any other method that isconvenient. In examples where friction welding is employed, weldingflash may be formed adjacent the mating surfaces 114, 116, 118, 120, asillustrated above. In one exemplary illustration, a weld flashingextending radially inwardly from the radially inner mating surfaces 116,120 may form a single weld curl 124 extending radially inwardly andaxially upwardly. Process 600 may then proceed to block 610.

At block 610, an outer contour of the piston 100 may be formed. Forexample, as described above, the pre-finished piston assembly 100′ maybe machined to form the combustion bowl 122 and/or ring belt portion106. Moreover, the machining of outer surfaces of the pre-finishedpiston assembly 100′ may remove weld flashing disposed on outer surfacesof the pre-finished piston assembly 100′.

The resulting shallow bowl construction of the piston 100 mayadvantageously allow for smaller overall geometry of the piston 100.Compression height, overall height of the piston, and a height of thecombustion bowl 122 with respect to top surface 160 may be reduced.Moreover, the smaller compression height reduces size and weight of thepiston 100, allowing smaller engine blocks and smaller componentsoverall, allowing greater freedom in vehicle packaging around the engineblock. A longer connecting rod may also be employed where compressionheight is minimized, reducing lateral forces during engine operationagainst the engine bore, thereby reducing friction between the piston100 and the bore, and improving engine efficiency.

With regard to the processes, systems, methods, heuristics, etc.described herein, it should be understood that, although the steps ofsuch processes, etc. have been described as occurring according to acertain ordered sequence, such processes could be practiced with thedescribed steps performed in an order other than the order describedherein. It further should be understood that certain steps could beperformed simultaneously, that other steps could be added, or thatcertain steps described herein could be omitted. In other words, thedescriptions of processes herein are provided for the purpose ofillustrating certain embodiments, and should in no way be construed soas to limit the claimed invention.

Accordingly, it is to be understood that the above description isintended to be illustrative and not restrictive. Many embodiments andapplications other than the examples provided would be upon reading theabove description. The scope of the invention should be determined, notwith reference to the above description, but should instead bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. It isanticipated and intended that future developments will occur in the artsdiscussed herein, and that the disclosed systems and methods will beincorporated into such future embodiments. In sum, it should beunderstood that the invention is capable of modification and variationand is limited only by the following claims.

All terms used in the claims are intended to be given their broadestreasonable constructions and their ordinary meanings as understood bythose skilled in the art unless an explicit indication to the contraryin made herein. In particular, use of the singular articles such as “a,”“the,” “said,” etc. should be read to recite one or more of theindicated elements unless a claim recites an explicit limitation to thecontrary.

What is claimed is:
 1. A pre-finished assembly for making a piston,comprising: a lower part defining a longitudinal axis, the lower parthaving a skirt and forming a lower surface of a cooling gallery, thelower part having a radially inner bowl surface defining a lower partradially inner mating surface, the radially inner bowl surface extendingfrom a radially innermost edge of the radially inner mating surfacetoward a center portion of the assembly, the lower part including aradially outer wall defining a radially outer mating surface; and anupper part having a radially outer bowl surface meeting the radiallyinner bowl surface at a radially inner joint, the upper part including aradially inner wall defining a lower surface extending radially todefine an upper part radially inner mating surface, the radially innerwall defining a radially inwardly facing surface leading upwardly awayfrom the upper part radially inner mating surface, the upper partincluding a radially outer wall defining an upper part radially outermating surface; wherein the radially inwardly facing surface of theupper part defines a non-parallel angle with the radially inner bowlsurface where the radially inner bowl surface meets a radially innermostedge of the radially inner mating surface of the upper part; wherein theupper part radially inner mating surface is defined by an upper partradially inner wall having a first radial width corresponding to theupper part radially inner mating surface and wherein the radially innerbowl surface of the lower part defines a second radial width greaterthan the first width.
 2. The pre-finished assembly of claim 1, whereinthe upper part radially inner mating surface is defined by an upper partradially inner wall having a first radial width corresponding to theupper part radially inner mating surface; and wherein the radially innerbowl surface of the lower part extends away radially inwardly from theupper part radially inner wall.
 3. The pre-finished assembly of claim 1,wherein the radially inner mating surfaces are friction welded together.4. The pre-finished assembly of claim 1, wherein the radially outermating surface of the upper part are joined with the radially outermating surface of the lower part such that the cooling gallery issubstantially enclosed.
 5. The pre-finished assembly of claim 1, whereina cooling gallery surface defined by the lower piston part and extendingfrom the radially inner mating surface of the lower piston part definesa first non-parallel angle with the piston axis.
 6. The pre-finishedassembly of claim 5, wherein the cooling gallery surface transitionsfrom the first non-parallel angle to a second non-parallel angle at aposition spaced axially below the radially inner mating surface of thelower piston part.
 7. The pre-finished assembly of claim 6, wherein thesecond non-parallel angle is greater than the first non-parallel angle.8. The pre-finished assembly of claim 7, wherein the first non-parallelangle is no greater than twenty (20) degrees, and the secondnon-parallel angle is no greater than forty-five (45 degrees.
 9. Thepre-finished assembly of claim 1, wherein the radially inner matingsurface of the lower part defines a substantially right angle withrespect to the piston axis.
 10. The pre-finished assembly of claim 1,wherein the radially inner mating surface of the lower part defines asubstantially right angle with respect to the radially inwardly facingsurface of the piston upper part.
 11. The pre-finished assembly of claim1, wherein welded material generated from the two radially inner matingsurfaces forms two weld curls extending radially outwardly from theradially inner mating surfaces.
 12. The pre-finished assembly of claim1, wherein the upper and lower parts are each formed of a steelmaterial.
 13. The pre-finished assembly of claim 1, wherein the upperand lower parts are each formed of a same material.
 14. The pre-finishedassembly of claim 1, wherein the radially inner mating surfaces arewelded together such that welded material generated from the tworadially inner mating surfaces forms only one weld curl extendingradially inwardly from the radially inner mating surfaces.
 15. A methodof joining a pre-finished assembly, comprising: providing a lower partdefining a longitudinal axis, the lower part having a skirt and forminga lower surface of a cooling gallery, the lower part having a radiallyinner bowl surface defining a lower part radially inner mating surface,the lower part including a radially outer wall defining a radially outermating surface; abutting the lower part against an upper part, the upperpart having a radially outer bowl surface meeting the radially innerbowl surface at a radially inner joint, the upper part including aradially inner wall defining a lower surface extending radially todefine an upper part radially inner mating surface, the radially innerwall defining a radially inwardly facing surface leading upwardly awayfrom the upper part radially inner mating surface, the upper partincluding a radially outer wall defining an upper part radially outermating surface; and welding the radially inner mating surfaces together,wherein the radially inwardly facing surface of the upper part defines anon-parallel angle with the radially inner bowl surface where theradially inner bowl surface meets a radially innermost edge of theradially inner mating surface of the upper part; wherein welding theradially inner mating surfaces together includes generating weldedmaterial from the two radially inner mating surfaces to form only oneweld curl extending radially inwardly from the radially inner matingsurfaces.
 16. The method of claim 15, wherein welding the radially innermating surfaces together includes friction welding the radially innermating surfaces.
 17. The method of claim 15, further comprisingestablishing the radially inner bowl surface of the lower part asextending away radially inwardly from the upper part radially innerwall.
 18. The method of claim 15, further comprising establishing acooling gallery surface defined by the lower piston part as extendingfrom the radially inner mating surface of the lower piston part todefine a first non-parallel angle with the piston axis.
 19. The methodof claim 18, further comprising establishing the cooling gallery surfaceas transitioning from the first non-parallel angle to a secondnon-parallel angle at a position spaced axially below the radially innermating surface of the lower piston part.
 20. The method of claim 19,wherein the second non-parallel angle is greater than the firstnon-parallel angle.
 21. The method of claim 15, further comprisingestablishing the radially inner mating surface of the lower part asdefining a substantially right angle with respect to the piston axis.22. The method of claim 15, further comprising machining the radiallyinner and outer bowl surfaces to define a piston combustion bowlsurface, wherein the piston combustion bowl surface defines a maximumheight from a top surface of the piston, and a ratio of the maximumheight to a piston diameter is no greater than 15%.
 23. A pre-finishedassembly for making a piston, comprising: a lower part defining alongitudinal axis, the lower part having a skirt and forming a lowersurface of a cooling gallery, the lower part having a radially innerbowl surface defining a lower part radially inner mating surface, theradially inner bowl surface extending from a radially innermost edge ofthe radially inner mating surface toward a center portion of theassembly, the lower part including a radially outer wall defining aradially outer mating surface; and an upper part having a radially outerbowl surface meeting the radially inner bowl surface at a radially innerjoint, the upper part including a radially inner wall defining a lowersurface extending radially to define an upper part radially inner matingsurface, the radially inner wall defining a radially inwardly facingsurface leading upwardly away from the upper part radially inner matingsurface, the upper part including a radially outer wall defining anupper part radially outer mating surface; wherein the radially inwardlyfacing surface of the upper part defines a non-parallel angle with theradially inner bowl surface where the radially inner bowl surface meetsa radially innermost edge of the radially inner mating surface of theupper part; and wherein the radially inner mating surfaces are weldedtogether such that welded material generated from the two radially innermating surfaces forms only one weld curl extending radially inwardlyfrom the radially inner mating surfaces.